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Prerequisite for PIM Dense Mode State Refresh

You must have PIM dense mode enabled on an interface before configuring the PIM Dense Mode State Refresh feature.

Restrictions on PIM Dense Mode State Refresh

All routers in a PIM dense mode network must run a software release that supports the PIM Dense Mode State Refresh feature to process and forward state refresh control messages.

The origination interval for the state refresh control message must be the same for all PIM routers on the same LAN. Specifically, the same origination interval must be configured on each router interface that is directly connected to the LAN.

Information About PIM Dense Mode State Refresh

PIM Dense Mode State Refresh Overview

The PIM Dense Mode State Refresh feature is an extension of the PIM Version 2 multicast routing architecture.

PIM dense mode builds source-based multicast distribution trees that operate on a flood and prune principle. Multicast packets from a source are flooded to all areas of a PIM dense mode network. PIM routers that receive multicast packets and have no directly connected multicast group members or PIM neighbors send a prune message back up the source-based distribution tree toward the source of the packets. As a result, subsequent multicast packets are not flooded to pruned branches of the distribution tree. However, the pruned state in PIM dense mode times out approximately every 3 minutes and the entire PIM dense mode network is reflooded with multicast packets and prune messages. This reflooding of unwanted traffic throughout the PIM dense mode network consumes network bandwidth.

The PIM Dense Mode State Refresh feature keeps the pruned state in PIM dense mode from timing out by periodically forwarding a control message down the source-based distribution tree. The control message refreshes the prune state on the outgoing interfaces of each router in the distribution tree.

How to Configure PIM Dense Mode State Refresh

Configuring PIM Dense Mode State Refresh

There are no configuration tasks for enabling the PIM Dense Mode State Refresh feature. By default, all PIM routers that are running a Cisco IOS XE software release that supports the PIM Dense Mode State Refresh feature automatically process and forward state refresh control messages.

To disable the processing and forwarding of state refresh control messages on a PIM router, use the ippimstate-refreshdisableglobal configuration command. To enable state refresh again if it has been disabled, use the noippimstate-refreshdisableglobal configuration command.

The origination of state refresh control messages is disabled by default. To configure the origination of the control messages on a PIM router, use the following commands beginning in global configuration mode:

Command

Purpose

Router(config)# interfacetypenumber

Specifies an interface and places the router in interface configuration mode.

Configures the origination of the PIM Dense Mode State Refresh control message. Optionally, you can configure the number of seconds between control messages by using the interval argument. The default interval is 60 seconds. The interval range is 1 second to 100 seconds.

Verifying PIM Dense Mode State Refresh Configuration

Use the showippiminterface [typenumber] detail and the showippimneighbor [interface] commands to verify that the PIM Dense Mode State Refresh feature is configured correctly. The following output of the showippiminterface [typenumber] detail command indicates that processing, forwarding, and origination of state refresh control messages is enabled.

The following output from the showipmroute command displays are the resulting prune timer changes for GigabitEthernet interface1/0/0 and multicast group 239.0.0.1. (The following output assumes that the debugippim privileged EXEC command has already been configured on the router.) In the first output from the showipmroute command, the prune timer reads 00:02:06. The debug messages indicate that a PIM Dense Mode State Refresh control message is received and sent on Ethernet interface 1/0, and that other PIM Dense Mode State Refresh routers were discovered. In the second output from the showipmroute command, the prune timer has been reset to 00:02:55.

RFCs

No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.

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